The enrichment of natural radionuclides in oil shale-fired power plants in Estonia--the impact of new circulating fluidized bed technology

Taavi Vaasma; Madis Kiisk; Tõnis Meriste; Alan Henry Tkaczyk

doi:10.1016/j.jenvrad.2014.01.002

The enrichment of natural radionuclides in oil shale-fired power plants in Estonia--the impact of new circulating fluidized bed technology

J Environ Radioact. 2014 Mar:129:133-9. doi: 10.1016/j.jenvrad.2014.01.002. Epub 2014 Jan 21.

Authors

Taavi Vaasma¹, Madis Kiisk², Tõnis Meriste³, Alan Henry Tkaczyk²

Affiliations

¹ Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia. Electronic address: taavi.vaasma@ut.ee.
² Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia.
³ Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.

PMID: 24462922
DOI: 10.1016/j.jenvrad.2014.01.002

Abstract

Burning oil shale to produce electricity has a dominant position in Estonia's energy sector. Around 90% of the overall electric energy production originates from the Narva Power Plants. The technology in use has been significantly renovated - two older types of pulverized fuel burning (PF) energy production units were replaced with new circulating fluidized bed (CFB) technology. Additional filter systems have been added to PF boilers to reduce emissions. Oil shale contains various amounts of natural radionuclides. These radionuclides concentrate and become enriched in different boiler ash fractions. More volatile isotopes will be partially emitted to the atmosphere via flue gases and fly ash. To our knowledge, there has been no previous study for CFB boiler systems on natural radionuclide enrichment and their atmospheric emissions. Ash samples were collected from Eesti Power Plant's CFB boiler. These samples were processed and analyzed with gamma spectrometry. Activity concentrations (Bq/kg) and enrichment factors were calculated for the (238)U ((238)U, (226)Ra, (210)Pb) and (232)Th ((232)Th, (228)Ra) family radionuclides and for (40)K in different CFB boiler ash fractions. Results from the CFB boiler ash sample analysis showed an increase in the activity concentrations and enrichment factors (up to 4.5) from the furnace toward the electrostatic precipitator block. The volatile radionuclide ((210)Pb and (40)K) activity concentrations in CFB boilers were evenly distributed in finer ash fractions. Activity balance calculations showed discrepancies between input (via oil shale) and output (via ash fractions) activities for some radionuclides ((238)U, (226)Ra, (210)Pb). This refers to a situation where the missing part of the activity (around 20% for these radionuclides) is emitted to the atmosphere. Also different behavior patterns were detected for the two Ra isotopes, (226)Ra and (228)Ra. A part of (226)Ra input activity, unlike (228)Ra, was undetectable in the solid ash fractions of the boiler. Most probably it is released to the surrounding environment.

Keywords: Activity balance; Atmospheric emission; Circulating fluidized bed boiler; Natural radionuclide; Oil shale; Radionuclide enrichment.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Coal Ash / analysis*
Estonia
Power Plants*
Radioisotopes / analysis*
Spectrometry, Gamma

Substances

Coal Ash
Radioisotopes